A filter press is known having a plurality of axially spaced filtering chambers each defined between a pair of filter cloths each in turn lying on a respective filter plate. The material to be filtered is introduced into the chambers between the cloths and the filtrate is withdrawn from between each cloth and the respective filter plate. The filtrant is removed by compressing it between the cloths periodically. This is achieved by displacing each of the filter plates inwardly into the respective filter chamber so that the filter cake on the respective filter cloth can be pressed against the filter cake of the other filter cloth of the respective chamber to form a relatively dry and easily removable block of filtrant. Such a filter press, which is described in the commonly owned U.S. Pat. No. 3,926,811 and commonly owned application Ser. No. 886,613 filed Mar. 14, 1978, allows the filter to be cleaned in a relatively simple manner, even automatically if desired.
The filter plates of such devices are typically the first parts to wear out. These plates are normally formed as an outer frame, an inner panel portion, and deflectable web structure between the inner panel and outer frame. The central panel is displaced axially relative to the frame for the pressing operation. During such displacement the web structure must deform. Most such plates are made of an at least limitedly elastically deformable synthetic resin so that they will be as long lasting and durable as possible. The disadvantage of this structure is, however, that such synthetic-resin material normally has little tensile strength. Thus the web structure can be deformed and compressed considerably, but when subjected to any tension beyond a certain relatively low limit such web structure normally will fail. As it is essential to maintain a closed chamber between each of the filter plates and the respective support plate, which may be a rigid support plate or another filter plate, any leakage through the web structure must be immediately repaired for proper operation of the device so that the area behind each of the filter plates can be filled with a fluid to displace the respective filter plate into the pressing position.
Such an arrangement works particularly well when the central panel of the filter plate is rigid. When, however, a relatively thin central panel is employed which is elastically deformable considerable tension is applied to the web structure. This is true even where the elastically deformable central panel is provided with a plurality of bosses to hold the filter cloth out for aspiration of the filtrate.